1 files changed, 29 insertions, 0 deletions
diff --git a/lib/utmp_io.c b/lib/utmp_io.c
new file mode 100644
index 0000000..1d8c423
--- /dev/null
+++ b/lib/utmp_io.c
@@ -0,0 +1,29 @@
+#include <unistd.h>
+#include <fcntl.h>
+#include <utmp.h>
+
+#define UTMP_SIZE (sizeof(struct utmp))
+
+/* type:  F_RDLCK or F_WRLCK */
+struct utmp *utmp_io(int fd, struct utmp *ut, int type) /*EXTRACT_INCL*/ {
+  int ret;
+  struct flock fl;
+  int (*op)() = (type==F_WRLCK) ? (int(*)())write : (int(*)())read;
+
+  fl.l_whence	= SEEK_CUR;
+  fl.l_start	= 0;
+  fl.l_len	= UTMP_SIZE;
+  fl.l_pid	= 0;
+  fl.l_type	= type;
+  
+  if (fcntl(fd, F_SETLKW, &fl)) return 0;
+  ret = op(fd, ut, UTMP_SIZE);
+
+  fl.l_start	= -UTMP_SIZE;
+  fl.l_type	= F_UNLCK;
+
+  fcntl(fd, F_SETLK, &fl);
+
+  if (ret != UTMP_SIZE) return 0;
+  return ut;
+}